The present invention relates to a new method and system for removing particulate and non-volatile residue (NVR) from the surfaces of manufactured parts. More particularly the present invention relates to a method and system of high velocity fluid jetting for removing residues from the surface of high precision manufactured products such as computer chips and computer disk platters in a reduced pressure environment. The examples used describe methods for internal and external surface treatment and can be used in many industries, which require contaminant and particle free parts as part of their everyday manufacturing process.
In the computer chip manufacturing industry, cleaning and particle removal, prior to etching and deposition, is becoming more of a challenge because of the sizes and aspect ratios encountered during the manufacturing of chips for high-speed computers. Particle removal of particle sizes less than 0.2 microns is becoming more the normal requirement to ensure quality chips and the particle removal process is becoming more and more critical to the process success. Fluids are the preferred media used for particle removal from chips, however, hand wiping is now often required to attain the desired particle removal level. The problem with fluid removal methods is the need to produce significant fluid motion near the solid surface where the micron size particles reside. Even during periods of rapid fluid motion across a solid surface, a viscous sub-layer exists in which there is very little fluid motion. This viscous sub-layer actually acts as a dampener to turbulent eddies moving toward the surface which would normally remove the particles submerged in this fluid viscous sub-layer if not inhibited by this fluid barrier. These layers also dampen the fluid motion from energy release mechanisms such as that produced by ultrasonic transducers which generate energy from imploding vapor bubbles in the fluid at relatively remote regions from the solid surface and viscous sub-layer.
Generally speaking, as a fluid moves across a surface, a layer of slow moving fluid near the solid surface prevents significant fluid impact forces on the surface, and thus inhibits the natural particle removal mechanism. The slower the fluid motion, the larger the viscous sub-layer and the greater the dampening of eddy fluid impact on a particle residing in this sub-layer. This sub-layer also dampens the eddies produced by ultrasound which if produced at a relatively far distance from the surface, dissipate their energy before reaching the surface when encountering this barrier sub-layer. Indeed, in order to circumvent this dampening problem, increased sound wave frequency is used in order to produce bubbles closer to the sub-layer and the particles. However, this enhancement is often offset by the fact that smaller bubbles release lower energy when imploded.
The main problem with the above particle removal mechanisms is that the fluid motion generated from the release of energy from imploding bubbles or from fluid eddies generated in turbulent fluid motion needs to penetrate through a relatively stagnant viscous sub-layer of fluid in order to reach micron sized particles residing within this sub-layer on the surface. The fluid motion is dampened to a level at which the energy imparted to the particle is no longer sufficient to overcome the adhesive or van der Waals forces holding these particles to the surface. It would therefore appear that there is a need for a process that carries out the impacting of fluid motion as a particle removing process in the absence of atmospheric interference or in a highly reduced atmosphere of stagnant fluid.
In this regard, the present invention is directed to a controlled environment processing chamber or chambers into which solvents, water and/or gases used for processing a material can be introduced. The process includes a means of applying a negative gauge pressure to the chamber to remove air or other non-condensable gases. Means are provided for introducing a solvent, solvent mixture, water or gas in either a liquid or vapor state. A first step removes soluble contaminants from the surface of an object being processed in the chamber using solvent(s) or solution(s). Treatment may be in the form of etching, cleaning, stripping, dissolving, penetrating, vapor degreasing, submerging, spraying, ultrasonic treatment or any other process in which material is removed from a solid surface to a liquid or gas phase. A second step further recovers residual solvent or solution from the object and chamber in order to reduce the atmosphere in the chamber. A third step introduces a fluid preferably in gas or vapor form which is jetted into the chamber in a fashion so as to be directed at a solid surface which may require the removal of insoluble material left behind after a pretreatment clean. A fourth step recovers any loose impediments or residual liquid or vapor from the chamber and returns the chamber to atmospheric pressure to remove the cleaned object.
In another aspect of the invention, a method of processing an object in an enclosed solvent processing system, including a solvent supply system in sealable communication with a cleaning chamber comprises the steps of:
(a) sealing the solvent or solution supply system with respect to the chamber;
(b) evacuating the supply system of air and non-condensable gases and maintaining this air free environment;
(c) opening the chamber to atmosphere and placing an object to be processed in the chamber;
(d) evacuating the chamber to remove air and other non-condensable gases;
(e) sealing the chamber with respect to atmosphere;
(f) opening the chamber with respect to the solvent supply system and introducing a solvent or solution into the evacuated chamber;
(g) processing the object while maintaining an air free environment within the chamber;
(h) recovering and processing the solvent or solution introduced into the chamber within the closed circuit processing system;
(i) introducing the solvent or non condensable gas as a jet of liquid, gas or vapor to further process the object by mechanically removing residual insoluble material from the surface by impact or drag forces on that material;
(j) recovering and processing the 2nd solvent or gas introduced into the chamber within the closed circuit processing system;
(k) repeating steps (i) and (j) as required;
(l) sealing the chamber with respect to the solvent supply system closed circuit solvent processing system;
(m) introducing air or other non condensable gases into the chamber for sweeping further solvent on the object and within the chamber; and
(n) opening the chamber and removing the treated object.
The primary objective of the present invention is to provide an environment conducive to the removal of insoluble material from objects requiring surfaces that are free of foreign material before further processing of the object. Once an environment is created which is either free or substantially reduced of fluids normally encountered at ambient conditions, the invention provides for a means of impacting a jet of fluid on a surface for the purpose of mechanically scrubbing the surface of particles and other insoluble foreign residue.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.